Discover refactor

This is just so we can track progress/what's left to do on this branch.

(anyone feel free to jump in and edit this list)
- [x] Make sure all search plugins have been updated to use entry
- [x] Get rid of 'type' option and just return all results for other filters to deal with?
- [x] If above is done, can we remove the comparators and just do the matching in urlrewrite search?
- [x] Above was done, now we need to do some filtering of search results in urlrewrite_search
- [x] Automatic staggering of search intervals to avoid many searches all in one run

There's probably more stuff too.

Oh, and I added some tests for discover, it should be fairly easy to add new ones to test more functionality as we decide on it now.